RFR: 8286395: Address possibly lossy conversions in java.security.jgss

[Ryan Ernst]

Applied required casts in java.security.jgss for the upcoming warning.
Verified by cherry-picking @asotona's patch.

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Commit messages:
 - 8286395: Address possibly lossy conversions in java.security.jgss

Changes: https://git.openjdk.org/jdk/pull/9204/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9204&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8286395
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/9204.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9204/head:pull/9204

PR: https://git.openjdk.org/jdk/pull/9204